As a new eco-friendly thermoelectric material, copper tin sulfide (Cu2SnS3) ceramics were experimentally studied by Zn-doping. Excellent electrical transport properties were obtained by virtue of 3-dimensionally conductive network for holes, which are less affected by the coexistence of cubic and tetragonal phases that formed upon Zn subsitition for Sn; a highest power factors ~0.84 mW m−1 K−2 at 723 K was achieved in the 20% doped sample. Moreover, an ultralow lattice thermal conductivity close to theoretical minimum was observed in these samples, which could be related to the disordering of atoms in the coexisting cubic and tetragonal phases and the interfaces. Thanks to the phonon-glass-electron-crystal features, a maximum ZT ~ 0.58 was obtained at 723 K, which stands among the tops for sulfide thermoelectrics at the same temperature.

Mohite-type ternary sulfide Cu2SnS3, which has been intensively studied in the photovoltaic field, has recently attracted much attention as an outstanding p-type eco-friendly thermoelectric material.

We report on the thermoelectric (TE) performance of intrinsic n-type AgBiSe2, a Pb-free material with more earth-abundant and cheaper elements than intrinsic p-type homologous AgSbTe2. Pb doping changes n-type AgBiSe2 to p-type but leads to poor electrical transport properties. Nb doping enhances the TE properties of n-type AgBiSe2 by increasing the carrier concentration. As a result of the intrinsically low thermal conductivity (0.7 W m(-1) K(-1)), low electrical resistivity (5.2 mΩ cm), and high absolute Seebeck coefficient (-218 μV/K), the TE figure of merit (ZT) at 773 K is significantly increased from 0.5 for solid-state-synthesized pristine AgBiSe2 to 1 for Ag0.96Nb0.04BiSe2, which makes it a promising n-type candidate for medium-temperature TE applications.